1. Field of the Invention
The present invention relates to an optical switch having movable optical switching elements, and more particularly to monitoring and controlling temperature variations of micro-machined micro-mirrors in an optical switching device.
2. Description of the Related Art
Increasing demands for high-speed Internet service and wireless communications are soon expected to outstrip current telecommunications capacity. Because optical fiber networks are capable of transmitting huge volumes of data at blinding speeds, telecommunications carriers are turning to optical fiber networks in an effort to meet future needs.
In order to implement tomorrow""s optical fiber networks, the telecommunications industry needs new optical devices that are inexpensive, efficient, and scalable to accommodate future optical telecommunications network expansion. Telecommunications providers prefer optical fiber networks that can be reconfigured quickly and efficiently. This gives the optical network the flexibility to accommodate growth and changes in future communications patterns. The ability to reconfigure quickly and efficiently also enables the network to restore failed communications by rerouting the communications to bypass the failure.
Optical fiber networks can be reconfigured at network nodes using optical switches to change the coupling between incoming optical fibers and outgoing optical fibers. Currently under development are optical switches that use movable micro-mirrors. These optical switches couple the optical signals between input and output fibers entirely in optical form, instead of converting the optical signals to electrical signals, switching the electrical signals, and converting the switched electrical signals back to optical signals.
To successfully operate such switches, the componentsxe2x80x94including fibers, lenses, and the micro-mirrorsxe2x80x94must be properly aligned and the angular position of the movable micro-mirrors must be precisely controlled. If the angular position of the movable micro-mirrors is off and/or if the other components are not properly aligned, some or all of the light from the input fibers will not reach the selected output fiber. At switching speeds needed for optical communication, a micro-mirror based switch must accurately and reliably move a mirror into position on command and hold maximum input-to-output optical coupling its position over long time scales.
In an optical switch utilizing movable micro-mirrors, beams of light are switched by reflecting the light beams off surfaces of steerable micro-mirrors. For efficient and reliable switching, the mirror surfaces should be substantially free to target the reflected beams with minimal divergence and high precision. However, it has been found that the temperature of a structure supporting moveable micro-mirrors may adversely affect the geometry of the micro-mirrors. It also has been found that temperature gradients may be present across structures supporting moveable micro-mirrors in an optical switch. Temperature gradients cause differential micro-mirror shapes between regions at different temperatures and/or localized alteration of a micro-mirror shape. Depending on the temperature a micro-mirror acquires in either scenario, differences between the coefficients of thermal expansion of micro-mirror materials may cause a micro-mirror to curve into either a concave or convex shape.
Generally, the ambient temperature across a micro-mirror supporting structure may affect the radius of curvature of the its micro-mirrors. Changes in the radius of curvature of a micro-mirror may increase the optical loss of an optical switch by defocusing light beams reflecting off the mirror, and thus cause inefficient and/or inaccurate translation of a light beam in the switch from an input fiber to a selected output fiber.
As shown in FIG. 9a, a micro-mirror 22 operating within a stabilized temperature may have little or no curvature along axis 900. In some applications, micro-mirror 22 may have a predetermined curvature or operate with an acceptable level of curvature. Micro-mirror 22 may be formed of a semiconductor material 22-a, such as silicon, having a light reflecting coating 22-b formed on its upper surface. Because the upper surface of micro-mirror 22 has limited curvature, light rays 901 incident on the micro-mirror surface will be reflected with accuracy toward the intended target 902.
If material 22-a and coating 22-b have different coefficients of thermal expansion, one material forming the mirror, 22-a or 22-b, may expand to a greater extent than another material, 22-b or 22-a, and thus cause the mirror to curve or deform. FIG. 9b shows micro-mirror 22 operating at a temperature greater than the stabilized temperature. As illustrated in FIG. 9b, if a substantial curvature occurs in a micro-mirror 22, a portion of the incident rays 903 are directed away from the intended target 902. Thus, an increase in curvature may cause an increase in the number of rays failing to reach the intended target within the switch.
While the temperature of the overall switch package containing a mirror-supporting structure may be controlled effectively using known heat sinking methods, the mirror supporting structures within the package are subject to localized heating due to differences in local heat sink efficiency. For example, the entire mirror supporting structure temperature may rise or fall relative to other switch sections or portions. Temperature gradients across a surface of a mirror supporting structure also may arise from power dissipated in circuitry near, in, or on the mirror supporting structure, from optical power dissipated in more in some regions of the supporting structure than others, and/or from other conditions affecting the switch""s ambient environment.
Hence, for accurate and reliable optical switching, mirror-supporting structures in movable micro-mirror switches should be insensitive to temperature variations that would otherwise affect a desired optical signal path. Thus, there remains a need in the art for optical fiber switching systems that are responsive to changes in ambient temperature that may otherwise cause inefficient and inaccurate translation of light beams from input fibers to selected output fibers.
The present invention has been made in view of the above circumstances and has as an object to provide an efficient and reliable optical switch.
One aspect of the present invention is an optical switch system that maintains a substantially uniform temperature across an element of an optical switch.
Another aspect of the present invention is an optical switch having a structure for monitoring a temperature variation across an element of the switch.
Yet another aspect of the present invention includes a structure and method for adjusting the temperature of portions of a movable mirror assembly.
Additional aspects and advantages of the invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. The aspects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.